Sound attenuators can be used on the intake side of the compressor of an exhaust-gas turbocharger. Combustion air is compressed in the compressor, and the combustion air is subsequently supplied to the combustion chambers of an internal combustion engine. The compressor is driven by the exhaust-gas turbine of the exhaust-gas turbocharger. Sound attenuators can often additionally be provided with a filter. This is generally referred to as a filter-type sound attenuator.
The compressor inlet of a turbocharger generates noise which is made up substantially of so-called blade pass frequencies (rotational speed multiplied by the number of rotor blades of the compressor wheel) and a medium-frequency whooshing sound.
To attenuate the noise, use is made of intake sound attenuators. The aim of the sound attenuators is to attenuate the noise in certain frequency ranges and supply the flow with the desired flow profile to the compressor.
High frequencies to be attenuated require either small gaps between the attenuation elements, or diversions, in order to prevent the high frequencies from passing through. The slightly lower frequencies require greater absorption thicknesses in order for them to be attenuated in an effective manner.
Known sound attenuators can therefore either be formed with a multiplicity of inserted attenuation elements, which can be curved in order to prevent the pass-through effect, or have a lining, which is flush with a wall, and one or more diversions.
For example, EP 0574605 A1 discloses a filter-type sound attenuator which is composed of a cast monoblock. The attenuation elements can be arranged in the grooved radial ribs of the cast monoblock. A filter frame composed of a removable perforated plate part surrounds the sound attenuator in such a way that the attenuation elements can be secured against falling out radially. The perforated plate part is arranged annularly around the sound attenuator by means of connecting elements. A disk-shaped attenuation element is composed of four attenuation segments which, when assembled, constitute an annular surface. An absorption element is held by two punched perforated plates and thus forms an attenuation element which is inserted radially into the grooves of the above-mentioned ribs of the cast monoblock.
EP 0740080 A2 discloses a filter-type sound attenuator which is in the shape of a circular cylinder and in which the attenuation elements can be arranged, with their attenuation surfaces parallel to the central axis of the filter-type sound attenuator housing which is likewise cast as a monoblock, in grooves of the housing walls. The attenuation elements can be composed of an attenuation plate which encases an absorption element. When in the mounted state on the circumference of the filter-type sound attenuator, the attenuation plates, together with the coarse filter segments arranged thereon, form a coarse filter ring that is surrounded by an annular filter.
JP 2002-4964 discloses a filter-type sound attenuator having a multiplicity of cylindrical attenuation elements which can be arranged coaxially one inside the other and through which flow passes in an axial direction and which, to prevent the pass-through effect, can be of undulating form. A filter element is arranged on the inlet-side axial face side.
KR 2008-8664 discloses a filter-type sound attenuator having a multiplicity of conical attenuation elements which can be arranged coaxially one inside the other and through which flow passes obliquely with respect to the axial direction oriented flow ducts. The attenuation elements can be held by a holding plate that extends perpendicular to the flow direction. A filter element is arranged on the inlet-side face side.